Histological types of brain tumors diagnosed at the Kenyatta National Hospital between 2016 and 2019: a retrospective study

Purpose To determine the histological types of brain tumors diagnosed at the Kenyatta National Hospital, Nairobi, Kenya. Methods This retrospective study retrieved patient-archived records at the Kenyatta National Hospital for the period 2016–2019. The histological types of brain tumors were assessed according to age, sex, and the WHO classification for CNS tumors using the GNU PSPP version 1.6.2-g78a33 software. Results were presented in tables and figures. Results During the study period, brain tumors appeared to increase gradually; however, there was a decline in 2018. During the study period, 345 brain tumor records were retrieved. Data on age were missing 33 records; hence, 312 records were included for age analyses. The mean age for the pediatrics and adults was 9 (± 5 SD) and 45 (± 14 SD) years, respectively. 88 (28.2%) and 224 (71.8%) tumors were diagnosed among pediatrics and adults, respectively. Most tumors, 60 (19.2%) were reported in patients aged ≤ 10 years, followed by 55 (17.6%), 48 (15.4%), and 47 (15.1%) in patients aged 31–40, 51–60, and 41–50, years, respectively. In both pediatrics and adults, most tumors were diagnosed in females aged ≤ 10 years and 31–40 years, respectively. Overall, two peaks were observed in patients aged 5–15 years and 40–45 years. Gliomas, 43 (48.9%) and medulloblastomas, 21 (23.9%) were the most common tumors in pediatrics, whereas meningiomas, 107 (47.8%) and gliomas, 70 (31.3%) were the most common tumors in adults. Most pediatric and adult tumors were benign with 50 (56.8%) and 157 (70.1%) cases, respectively. Low-grade gliomas and medulloblastomas were the commonest benign and malignant tumors among pediatrics, with 31 (62%) and 21 (55.3%) cases, respectively. Conversely, meningiomas and high-grade gliomas were the most common benign and malignant tumors in adults, with 106 (67.5%) and 44 (65.7%) cases, respectively. Conclusion This study highlights the existing burden of brain tumors in Kenya and data from KNH may be representative of the national burden of BTs. This study lays a foundation for subsequent clinical and epidemiological studies and emphasizes the need to adopt existing reporting standards to help realize a complete picture of the burden of brain tumors in Kenya.

There was a bimodal distribution of the brain tumors with peaks at 5-15 years and 40-45 years (Fig. 2).

Assessment of brain tumors according to sex
Of 345 cases, 190 (55.1%) were diagnosed in females, while 155 (44.9%) were diagnosed among males.Cumulatively, meningiomas were the most prevalent tumors followed by gliomas, medulloblastomas, brain metastasis and pituitary

Distribution of meningiomas according to age and sex
Of all tumors assessed by age, 110 were meningiomas.85 (77.3%) were diagnosed in female patients, whereas 25 (22.7%) were diagnosed in male patients.Among females, most, 25 (29.4%)cases were reported in patients aged between 31 and 40 years, followed by those between 41 and 50 years, with 21 (24.7%)cases.Among males, 7 (28%) cases were reported in patients aged 51-60 years, followed by those between 31 and 40 years with 6 (24%) cases (Table 6).

Discussion
In this study, brain tumor cases showed an increasing trend over the years.The highest number of cases was reported in 2019; whereas a decline was observed in 2018.The low cases prior to 2019 may be attributed to various challenges at the institutional and health system challenges, including inadequate ICU beds, fewer surgery days due to less theaters available for neurosurgery, prioritization of other surgical emergencies over elective neurosurgeries, and sporadic nationwide health service disruption due to industrial actions [24].Subsequently, dedicated neurosurgical theaters were set up with daily neurosurgery electives, which may explain the higher cases in 2019.However, these cases may not reflect the true burden of BTs in Kenya considering KNH remains the main neurosurgical and neurooncological care center.Patient factors, such as healthcare seeking behaviors, health system challenges, including service delivery, health workforce, health system financing, and neurosurgical and neurooncological care are largely overlooked in resource-limited settings, including Kenya [25].This may impair health care and service delivery for brain tumors.There is also an underinvestment in healthcare infrastructure and brain tumor research in developing countries compared to developed countries [26].
There is acute shortage of comprehensive neurooncological care, including radiologists, neurooncologists, and neurosurgeons with dismal ratio of 1 neurosurgeon for 2.4 million people in East Africa, which Kenya is part of [27].All these challenges may explain the persistently low incidence rates reported in the African region [1,28].
In this study, the mean age for the pediatrics (≤ 20 years) and adults was 9 (± 5 SD) and 45 (± 14 SD) years, respectively.Most tumors, 71.8% tumors were diagnosed among adults.There was a bimodal distribution of the BTs with peaks at 5-15 years and 40-45 years.Most tumors, 60 (19.2%) were reported in patients aged ≤ 10 years, followed by 55 (17.6%),48 (15.4%), and 47 (15.1%) in patients aged 31-40, 51-60, and 41-50, years, respectively.In both pediatrics and adults, most tumors were diagnosed in females aged ≤ 10 years and 31-40 years, respectively.This study's mean age for pediatric BTs was relatively same to the current SEER report (United States), which reported a mean age of 8 years [29].However, the mean age varies significantly according to the specific childhood brain tumors (CBTs) [30].This study's mean for adult BTs is relatively similar to another study that was conducted at the same facility in 2014 that reported a mean of 40.63 ± 15.36 years [31].Generally, the distribution of BTs according to age was relatively similar to the local study cited above [31] and with the CBTRUS findings [32].In this study, two peaks were observed in both childhood and adulthood, like other studies [2,6].The bimodal incidence of BTs is attributed to the likelihood of certain BTs occurring at a certain age due to the associated biological, genetic, and environmental risk factors [2].Childhood tumors, such as embryonal tumors and astrocytomas, are more common in children and may have genetic predispositions [6,8,30].On the other hand, malignant gliomas, meningiomas, and pituitary adenomas are common in adults [6].Adult BTs are also associated with the relatively long duration of exposure needed for neoplastic transformation [2,8].Biological factors, such as hormones are attributed to high adult glioma and meningioma cases [8].In this study, BTs diagnosed in males were 46.2% versus 53.8% in females; thus, the overall male-to-female (M:F) ratio was 1:1.6.This compared unfavorably with other African studies that reported an M:F of 1:1 [33,34].This could be attributed to the relatively high frequency of meningiomas diagnosed in females in this study.Gliomas were most diagnosed in males, whereas meningiomas were the most diagnosed brain tumor type in females.Gliomas had M:F ratios of 1:1.1, whereas meningiomas had a M:F ratio of 1:3.4.These findings are consistent with local and international studies [31,35].
Gliomas and medulloblastomas were the most common pediatric tumors in this study.In addition to gliomas and medulloblastomas, other studies have reported craniopharyngiomas and ependymomas among the most frequent pediatric tumors [6].Most pediatric tumors in this study were benign, like other studies [36].In this study, gliomas were the most common benign pediatric BTs, whereas medulloblastomas were the most malignant brain pediatric tumors.Low-grade gliomas are the most common childhood tumors, and rarely become malignant [37].In this study, medulloblastomas were the second most frequent of all pediatric tumors, but the most common malignant childhood BTs and were most frequently diagnosed in males, like a current review on pediatric tumors studies [30].Medulloblastomas are the commonest component of the heterogenous group of malignant tumors known as CNS embryonal tumors [38].CNS embryonal tumors were previously categorized as primitive neuroectodermal tumors (PNETs); however, molecular characterization necessitated the reclassification [30].Ependymomas were the third most common tumors at 8% of all pediatric tumors in this study.This is similar to the generally reported frequency of approximately 5-10% [30].Some of the risk factors associated with pediatric tumors include genetic factors, exposure to ionizing radiation (IR), non-chromosomal structural birth defects, high socioeconomic position, and high birth weight [8,39].Genetic predisposition is a known risk factor in the occurrence of pediatric ependymomas, medulloblastomas and gliomas [8,30].However, low-grade gliomas with isocitrate dehydrogenase 1 gene (IDH1) and IDH2 mutations, which transform to malignancy are rarer in pediatrics [40].Longer telomere length and European ancestry are associated with increased risk for ependymomas [6].However, genetic association studies in CBTs have not been conducted in other tumors; hence, the contribution of genetic factors is unknown in these tumors [6].
Moderate to high radiation doses are known causes of brain tumors, including CBTs [8,39].However, the risk of developing brain cancer from low-dose diagnostic or therapeutic radiation is debatable.The carcinogenic effects of IR are heightened in children, particularly in younger children [8].Postnatal exposure to computed tomography was associated with increased risk for BTs [39].Childhood exposure to therapeutic radiation for leukemia is also associated with development of BTs in adulthood [8].Reverse causation may limit these findings as pediatrics with preexisting cancer or at a higher risk for cancer are likely to undergo computed tomography of the head [8].During pregnancy, exposure of the mother to diagnostic radiation is also thought to increase brain cancer risk [8].The tumors that may be induced by IR include gliomas and meningiomas [41].Generally, non-chromosomal structural birth defects are known risk factor for CBTs with more preponderance in children aged ≤ 5 years with cancer [8].CNS anomalies

Research
Discover Oncology (2024) 15:39 | https://doi.org/10.1007/s12672-024-00893-6 have a higher risk of CBTs.Birth weight > 4000 g is also associated with higher risk of pediatric embryonal tumors and astrocytomas [6].However, other studies reported no associations between birth weight and CBTs [42].There is limited evidence on the contribution of these risk factors to CBTs from low-resource settings, particularly Africa.Overall, most adult BTs cases in this study were reported in patients aged 40-60 years.High cases were reported in female patients between 31 and 60 years in this study.Meningiomas and gliomas accounted for most of the adult BTs, with a cumulative prevalence of 79.1%.This is like other studies, both locally [31,43] and globally [32,33,44].Most adult tumors were benign, with meningiomas being the most frequent.Meningiomas mostly occur in patients in their fourth and fifth decades of life, with more female cases than males [45].High-grade gliomas were the most frequent malignant adult tumors, followed by brain metastases.High-grade gliomas were most reported in males.In this study, metastatic tumors to the brain were the fourth most frequently reported of all tumors, with all cases in adults.This is consistent with other studies [31,33,46].The increased prevalence of brain metastases is attributed to improved cancer care, and thus, cancer patients live longer, with an estimated 20-40% likelihood of developing BTs [14].Increased access to imaging may also explain the increasing diagnosis of brain metastasis among cancer patients.The risk factors associated with adult BTs include genetic mutations, ancestry, increased leucocyte length, human leucocyte antigen (HLA) haplotypes, hormonal factors, environmental exposures, and higher socioeconomic status [6,47].On the contrary, some factors such as use of aspirin, statins, and history of respiratory allergies decrease the risk of adult BTs, particularly gliomas [8,48].Most risk association studies have been conducted in high-grade gliomas since they are the most frequent malignant BTs.Most tumors, particularly gliomas do not have a family history of glioma; however, approximately 5% are familial [8].Studies on genetic polymorphisms in gliomas and meningiomas, pituitary adenomas, and primary CNS lymphoma have found various single nucleotide polymorphisms associated with these BTs, particularly in the European and East Asian populations [6,49].Increased leukocyte telomere length has been implicated in meningiomas and gliomas [50,51].Neurofibromatosis type 2 (NF2) mutation is also associated with meningiomas [45].However, genetic studies are limited in Africa, including Kenya.
High-dose IR is one of the environmental exposure factors that has been widely evaluated in adult BTs and has been implicated in gliomas and meningiomas [6].However, this may not account for the high burden of adult BTs.Studies on other environmental exposures, including radiofrequency fields emitted by cellular phones, extremely low frequency (ELF) magnetic fields, electromagnetic fields (EMF) from power lines, and other non-radiation exposures have reported conflicting results or no associations with adult BTs [52,53].The contribution of these environmental exposure in Kenya is unknown.Higher socioeconomic position (SEP) has been linked to higher risk for adult BTs, particularly gliomas [54,55].This may be due to diagnostic bias where underreporting may occur in patients with lower SEP.Another explanation is that immune exposures, particularly allergy and infections and health-seeking behavior may be influenced by SEP [6,8].This may explain the varied burden of BTs between higher SEP and lower SEP settings, such as Kenya.Sex hormones are hypothesized to play role in the gender-associated prevalence in meningiomas and gliomas.Estrogen and progesterone are attributed to the high frequency of meningiomas in women [47,56].On the other hand, testosterone is implicated in the high glioma prevalence in males [57].Studies on the association of estrogen and progesterone and meningiomas in premenopausal and perimenopausal women have reported conflicting results [58].A population-based case-control study reported a marginal association between meningioma and exogenous hormone exposure from oral contraceptives and hormone replacement therapy.However, other studies found no association between meningioma and hormonal exposures [59,60].Other studies have reported protective role of endogenous hormones against meningiomas in premenopausal women [61].Glioblastomas, which comprise high-grade gliomas are associated with testosterone, whereas progesterone and estradiol are thought to protect against glioblastomas [57].Most associations studies between risk factors and brain tumors have been conducted in developed countries.Further research is needed, more so in low-resource settings to establish the association of risk factors to the existing pediatric and adult brain tumors.

Study limitations
This study was dependent on the completeness of the recorded data.There was a lack of data on some variables, including tumor location, ancestry/ethnicity, and race.In addition, the lack of immunohistochemical and molecular classification of brain tumors limited the comparison of these findings to international studies.

Fig. 1
Fig. 1 Figure showing trends in brain tumors between 2016 and 2019

Table 1
Distribution of brain tumors according to age and sex

Table 3
Distribution of pediatric brain tumors according to the WHO Classification of CNS tumors

Table 4
Distribution of adult brain tumors according to the WHO Classification of CNS tumors

Table 5
Distribution of gliomas according to age and sex